This invention generally relates to bio-fuels, and in particular to a system and method of deriving a fuel composition from biomass feedstocks in a integrated manner.
Increasing crude oil prices and increased environmental concerns have resulted in an increased interest in renewable energy sources. As is seen from the current direction of research, renewable resources like solar power and wind energy are used for production of electricity; whereas the fuels derived from biomass are predominantly used as transportation fuels.
In general, biomass such as wood and other plant biomass can be processed by two methods: biochemical methods such as fermentation; and thermochemical methods such as gasification. Biochemical methods use microorganisms to break down the biomass into simpler compounds such as ethanol. However these reactions are quite slow, and it can take at least several weeks to process a given batch. Due to factors like this, the biochemical processes, presently, are not in a state of direct industrial applicability.
Thermochemical methods involve processes such as biomass gasification, wherein the biomass is converted into syngas. The syngas is then transformed into various fuel compounds, using a variety of techniques such as Fischer Tropsch Techniques. These techniques are somewhat analogous to coal gasification, and the subsequent conversion to liquid fuels.
However, there are many differences between coal and biomass as a feedstock for gasification. As an example, due to the higher moisture content often present in biomass, a considerable amount of energy is required for drying the biomass. Biomass also has a larger amount of total volatile matter, as compared to coal. During gasification, the volatile matter is released at relatively lower temperatures.
A large part of this volatile matter is responsible for the tar formation during gasification of biomass. Tar levels in the product gas also depend on the gasifier configuration. In an updraft fixed bed gasifier that operates between about 300° C. and about 1000° C., the product gas contains up to 35000 ppm tar. In a downdraft configuration, the tar level in product gas is comparatively low, but still contains about 500 and about 1000 ppm tar. Depending on the gasifier configuration, tars tend to deposit on the walls of gasification equipment, or get transported downstream with the product gas. The tar deposits create the need for frequent maintenance, and may also reduce the operating life of the gasification equipment. The carryover of tar can deposit on and block filters, pipes, valves and turbochargers, leading to a decrease in performance. In some instances, elaborate cleaning systems are required to address these problems.
Other methods of using biomass sources to produce fuels involve producing oils from oilseeds and other feedstocks. These methods typically involve conversion to a diesel-like fuel, which is conventionally made by trans-esterification of oil derived from oilseeds, vegetable oils and animal fats. Trans-esterification involves a reaction with alcohol, and produces a mixture of esters of fatty acids. These fatty acid esters are typically called “biodiesel”. Biodiesel is better suited for fuel applications than pure oils and fats, due to more advantageous characteristics; such as flow properties, combustion properties and the like. However, the use of the fatty acid ester fuels can result in operating problems—especially at low temperatures. Hence the use of bio-diesel in colder regions may be somewhat limited.
Frequently, these fatty esters need to be upgraded by hydro-processing, prior to use, so as to improve the operating temperature limits. The upgrading techniques primarily involve saturation of double bonds, which improves the minimum working temperatures of the biodiesel, and improves properties such as cloud point, cold filter plugging point, and pour point.
Other methods of producing diesel-like-fuel from vegetable oil sources involve directly hydro-treating of the bio-oils. This results in the breakdown of the triglycerides, which are primary constituents of the bio-oils. The reaction with hydrogen also results in saturation of double bonds, thus producing diesel fuel mixtures, which have better operating ranges.
Although such methods as these use renewable sources like bio-oils, the process itself is not completely renewable, due to the need for external hydrogen, which is required in these reactions. Hydrogen is typically derived from steam methane reforming, which depends on methane, and is not normally considered a renewable source. Alternate methods of hydrogen production include the use of water electrolysis. This method requires electricity as one of the major inputs. However, most electricity is currently produced from fossil sources such as coal, or natural gas. Thus even this method of hydrogen production is not completely renewable.
Moreover, biodiesel as a transportation fuel is not usable in all types of vehicles, since the properties of biodiesel are much different than gasoline. Biodiesel can be used in locomotives and some cars that are designed to operate with diesel fuel. Another large outlet for fuel is the aviation sector, where the fuel is, commonly known as “jet fuel”. This sector also cannot readily use biodiesel.
With these considerations in mind, it is desirable to develop a method to produce fuel compositions such as jet fuel, from biological sources. It would also be very desirable to develop a solution to produce such fuel compositions from renewable sources, using a truly renewable process.